Laying out mechanical, electrical and plumbing systems in new buildings under construction, or in existing buildings undergoing renovations or additions, is tedious, time consuming, and expensive. Typically, it has required a significant amount of labor to lay out construction points at a construction site on walls and on other generally vertical surfaces, so that cuts can be made to permit the passage of pipes, conduits and the like through the walls and other generally vertical surfaces and to permit the installation of various switches, fittings and similar devices. This layout process has required teams of workers that measure and mark the locations of these construction points, with much of the work being accomplished manually.
A number of factors increase the difficulty of this manual layout process. Actual walls at a construction site may not be located precisely where construction plans indicate. Walls may be curved, angled (i.e., not perpendicular to the penetrating system), or tilted vertically, either by design or simply as a result of being inadvertently out of plumb. If the system penetrating the wall is sloped (e.g., a downward sloping drain pipe), the elevation of the system at the penetration location will change, depending on the actual location of the wall. Similarly, if the system penetrating the wall is angled to the right or left, the horizontal location of the system at the penetration location will change, depending on the actual location of the wall. The data defining the location of the system penetrating the wall may not include a design point precisely at the wall surface, or the location where the construction plans indicate the wall surface should be located may be in error.
Manually measuring and accounting for all of these variables to locate construction points on walls and other vertical surfaces is very difficult and very time consuming. This process is also subject to errors, both from measurement mistakes and from accumulated errors which compound as successive measurements are made going from one intermediate point to the next. Further, building designs and requirements have become more complex, and construction schedules have become tighter, adding to the need to facilitate and simplify the layout process.
Total stations have been used in the past both for outdoor surveying, and for machine control. In a typical surveying application, a total station, positioned at a known location, directs a beam of laser light to a target positioned by a surveyor at a point to be surveyed. The target may include retroreflectors which reflect the beam back to the total station. By measuring the time of flight of the beam, the distance between the total station and the target is determined. By also measuring the direction of the beam from the total station to the target, i.e., the altitude and azimuth angles that define a vector from the total station to the target, the location of the target can be precisely determined.
Robotic or automated total stations have been developed that are capable of locating and tracking a target without being attended by an operator, and without requiring that the target have a retroreflective surface. Further, such automated total stations can be controlled to point in precisely determined directions. A total station can point to surfaces throughout a worksite and, by detecting the light reflected from those surfaces, determine the three dimensional coordinates of the illuminated points throughout the worksite in relation to the position of the total station. If the coordinates of the total station are known, the coordinates of the illuminated points are also known.
A method of using an automated total station to facilitate layout of a series of points at an indoor construction site on a horizontal surface, such as a floor or a ceiling, is disclosed in U.S. patent application Ser. No. 12/274,876, filed Nov. 20, 2008, published as Publication No. US-2010-0123892, which is assigned to the assignee of the present application. The entire disclosure of Publication No. US-2010-0123892 is incorporated herein by reference. This method takes into account unexpected ceiling and floor locations by illuminating with a laser beam of visible light from a total station a construction point on the surface that has the same horizontal position coordinates (i.e., x and y coordinates) as the selected construction point on the ceiling or floor of nominal elevation. It is desirable to be able to lay out construction points precisely on generally vertical surfaces at a construction site, as well, and to have the ability to accommodate vertical surfaces that are not located precisely as anticipated, and are not precisely vertical.